This invention is generally in the field of light emitting structures, and relates to a light emitting device and a display device utilizing the same. The invention is particularly useful in three dimensional displays utilizing differently polarized light generated by modulated down converted emission from nanoparticles.
Polarization properties of light are used in a variety of optical applications (products and methods) ranging from flat panel liquid-crystal displays (LCDs) to microscopy, metallurgy inspection and optical communication. Most available light sources generate unpolarized light, and selection of specific polarization of light is typically done using polarizers of various types. The selection of a particular polarization using a polarizer usually comes at the cost of energy loss; approximately 50% of impinging light may be lost when using a simple passive (non-emissive) polarizer to provide polarized illumination using a non-polarized light source.
Efficient polarization selection of light emitted by an unpolarized light source can be achieved by locating passive (non-emissive) polymer films in the optical path of the emitted light. These films may recycle some of the light and thus enhance the transmission of light of the desired polarization. Recycling of light is based on reflecting light components of unwanted polarization onto a reflecting surface, thereby producing multiply reflected light components which depolarize after subsequent reflections, and thus at least some light components are transmitted after each reflection. However, such passive systems are complex and expensive to produce, as multiple layers are required for efficient light recycling. Another “passive” approach to recycling a backlight output through a polarizer uses a reflective nanowire grid polarizer (Ge, Zhibing and Wu, Shin-Tson. “Nanowire grid polarizer for energy efficient and wide-view liquid crystal displays.”, Applied Physics Letters, 93, 121104, 2008).
Passive approaches as described above complicate the design of a backlight system and are expensive. They are also inactive in enhancing the quality of the color gamut of the emitted light, because they are wavelength dependent. In fact, the need to preserve the color gamut of the original backlight complicates further the layer structure of backlight system.
Anisotropic (elongated) nanoparticles such as nanorods (also at times referred to herein as “rods”) are known as being capable of providing polarized emission. This is also described in WO 2010/095140 assigned to the assignee of the present application.
To this end WO 2010/095140 describes an optical display device and a method for use in displaying an image. The optical display device comprises An optical display device comprising: at least one region of nanostructures operable as an optically active media, such that said nanostructures are responsive to input electromagnetic radiation to emit output electromagnetic radiation, and an arrangement of electrodes being configured and operable to be selectively addressable to create an external electric field to said at least one region of nanostructures, said region of nanostructures and said arrangement of electrodes defining together a pixel arrangement of said display device; said external electric field affecting said at least one region of nanostructures to selectively modulate emission of said output electromagnetic radiation, said output electromagnetic radiation being an output of at least one pixel element of the display device. Some nanorod systems providing polarized emission are described in the following publications:
X. Peng et al., “Shape control of CdSe nanocrystals”, Nature 404, 59-61, 2000 describes colloidal based semiconductor core (without shell) CdSe nanorods embedded in a polymer. Nearly full polarization can be obtained from single rods.
T. Mokari and U. Banin, “Synthesis and properties of CdSe/ZnS rod/shell nanocrystals”, Chemistry of Materials 15(20), 3955-3960, 2003 describes the emission enhancement of rods by growing a shell on the rod structure.
D. V. Talapin, et al, “Seeded Growth of Highly Luminescent CdSe/CdS Nanoheterostructures with Rod and Tetrapod Morphologies”, Nano Letters 7(10), pp 2951-2959, 2007 describes a quantum yield improvement achieved for seeded nanorod particles.
C. Carbone et al, “Synthesis and Micrometer-Scale Assembly of Colloidal CdSe/CdS Nanorods Prepared by a Seeded Growth Approach”. Nano Letters, 7(10), pp 2942-2950, 2007 describes a dipole pattern emission of seeded rods, i.e. emission emanating from the rod center rather than its tips.
Three-dimensional (3D) display systems provide a huge enhancement to video viewers. The currently available 3D display systems utilize two main methods, one is based on polarization of light and the second is based on sequential display.
Projection of a 3D image by providing a first image, to be viewed by one of the viewer's eyes, in one polarization state and a second image, to be viewed by the second eye, in an orthogonal (e.g. perpendicular) polarization state is especially used in movie cinemas. The film is simultaneously projected onto a screen utilizing two projectors, each providing images in one polarization state, projecting two separate films on the two eyes of the viewer. The viewers need to use a related polarized eye glasses which are configured such that each of the eyes receive only the corresponding images. For example, the right eye-glass includes a polarizer blocking light of one polarization state and transmitting light of the orthogonal polarization state, and the left eye-glass includes the orthogonal polarizer.
Alternatively, alternating display of images is typically used in television displays and similar devices. The pictures for each eye are displayed sequentially (left, then right, then left, then right again and so on). The viewers have to wear an active shutter glasses device, which synchronically transmits light to one eye and blocks light from reaching to the second eye in accordance with the display sequence.